. >>> we're learning more about the events that led to the resignation of cia director general david petraeus. it began with an fbi investigation of harassing e-mails from petraeus' biographer paula broadwell. those e-mails were sent to 37-year-old joe kelly, a state department liaison and friend of general petraeus. sources say the fbi stumbled onto the affair between petraeus and broadwell during that investigation and according to a former petraeus staffer who spoke to the general today, the affair began after he became cia director and ended about four months ago. brian moore is covering this developing story tonight from capitol hill. >> reporter: as president obama saluted vets transin arlington investigation cemetery. >> to thank you, to honor you. >> reporter: washington was consumed with the thought of one of the nation's most celebrated military heroes, cia director and former general david petraeus stepped down over an extramarital affair. >> it was like a lightning bolt. >> reporter: nbc news reports personal e-mails between petraeus and biographer paula broadwell came to